This Core will support all Projects of this program project by providing flow cytometry services and by performing in vitro functional assays to monitor the immune status of subjects participating in clinical trials. For the clinical trials, the Core will be used to document the development of T cell tolerance to donor or host alloantigens, and assess the ability of the reconstituted patients to mount an immune response to newly introduced as well as recall antigens. For all four Projects the Core will provide flow cytometry based cellular phenotype analysis including the determination of adequate host T cell depletion and the monitoring of T cell recovery following hematopoietic progenitor cell transplantation for the patients in the clinical trials.